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A stiffer bike is only really advantageous in a sprint like effort. Problem is that you have to get to the sprint point and if your fatigued over a long distance on a stiff bike then your not going to be able to deliver much power into your sprint.

If your racing in a crit or your the designated sprint guy for your team then you want a stiff bike, otherwise your probably better off with a more comfortable ride...especially if your doing longer distances.

With over 25 years of riding and racing I have a large stable of road bikes so I can pick out the best bike for the type of ride I plan on doing that day. If there was a fire and I only had time to save one bike; it certainly would not be my stiffest bike.

My second good bike when I started riding in the mid 80s, after a steel Raleigh, was a Vitus 979 aluminium. It was one of the lighter and cheaper good frames you could buy then. It used very small diameter aluminium tubes and an aluminium fork. It's famous for not being stiff at all. Mine is a 59cm, so it's extra flexy as Vitus did not use stiffer tubes for the larger sizes. I raced on it for 5 years. I didn't feel that the bike was holding me back. Then I rode it off and on after starting riding again in 2001. I put modern kit on it (8 of 9 on 7 since the rear triangle can't be spread) and used it as a rain/backup bike until recently.

So I have been able to compare it to modern bikes. Ride wise the vibration level is similar to modern carbon frames, except there is more vibration through the aluminium fork. When standing on a climb or sprinting you can feel the flex. But it doesn't feel slower, just different. I don't know if I buy Heine's description, but it does feel as though I can stay "on top" of a gear at a slightly lower rpm when standing on a climb. For all I know I'm imagining that as well. But I rather like it. If I was going to get a custom CF bike made I'd ask for a relatively flexy one. Maybe not as flexy as the 979, which is a little wierd on descents until you get used to it, but less stiff than my Cervelo R3SL.

I have yet to see an actual scientific study that shows that frame flex makes a bike slower. Perhaps this thread will cause one to be unearthed.

My take is that the "right" amount of flex/stiffness is fastest. In almost any ride/race on normal roads too stiff a bike will tend to skip a bit too flexy a bike will tend to wander, both mostly on turns or descents.

Other than cases like those and special things like PR Pave, I don't really think stiffness makes a bike faster or slowr, maybe more or less enjoyable.

Think we need to divide this discussion into drive line stiffness, torsional stiffness, and vertical stiffness.

And just like different saddles different riders will need different thinks.

I'm 100kg+ (that's all I'll own up to). I changed from a triple butt Al frame to a Cannondale System 6. MY GOD do I prefer the System 6 for so many reasons!!

The triple butted frame I could twist the square taper cranks and BB area enough to rub the chain on the FD when trying to sprint up a hill. When I changed to the System6 with BB30 sprinting up short steep hills became just the best fun in the world! It really felt like the torque I was putting out was rocketing me up the slope.So I'm sure if you are a high torque rider you will enjoy higher drive line stiffness. If you produce the same amount of power but through spinning you will flex the frame less so probably won't notice the same difference.

Torsional stiffness will mean the bike turns faster and more consistently because frame will resist the forces better to make the line change. There is a trade off that you don't want too stiff or the bike will chatter on a bump more and loose traction-not good. A smaller rider will not flex a frame as much, so will need a different sweet spot for sharp handling and forgiving flex. So you can't say stiffer is better, it comes down to the rider and their needs and how they like the feel.Reports were given that when Trek went to tapered head tubes that the madone even with the same geometry as old models turned a lot more sharply but still handled great at speed in a straighter line. That is the increased torsional stiffness.

Vertical stiffness. I think everybody would prefer a bit more vertical compliance. There could come a point where vertical softness results in sponginess but unlikely you'd ever find that on a road bike with HP tires.

All my serious cycling has been on steel, my current modern steel has no real noticeable flex, but a good CF bike does climb a bit better, around 3-5% after a test ride. Remember trying out a columbus SL TT bike back in the day on a hill and it rode like a blancmange- def slower!

Just for clarity, mechanical springs are generally extremely effecient. Whether the spring constant or modulus of that spring is high or low (stiff or soft), there is little heat generated. Same for a bike.

If Speed = Effiency, the the question is one of the human body, not the bike.

The Look 496 is very very very stiff(bottom bracket two time stronger than road bike for example and a little heavier than many other frames). I can tell you that you feel the difference when you want to push it or push it hard!! No flex at all; you feel that all your energy is use to go faster and not to flex the frame!!

But it's impossible(when i say impossible i mean IMPOSSIBLE) to ride it on cobblestones roads(If you want to make a milk shake it's probably a very good idea) and very difficult to ride on bad roads. My weight is 71kilo, imagine a 60 kilo rider...it would be like a rodéo...

I would recommend a stiff frame on good quality roads(stiffness-comfort), not on slope roads(heavier frame), for powerfull man(to take the benefits of the frame).

My experience is that stiffer bikes really do FEEL faster. ....and you notice that feeling right at first, when you are fresh and the sensation is new. But I doubt it is actually measurably faster in a sprint or any other distance.

After riding for a couple hours, you body may actually feel fresher and you may be able to put out more power if you have been riding something a little more flexy and comfortable. It should be noted that a lot of classic races have been won by the world's strongest professional cyclists on frames that I'm sure many frame connoisseurs would poo-poo as being "noodles". Just youtube some videos of Sean Kelly riding those aluminum Vitus frames in Paris Roubaix, Milan-San Remo, etc.

Coming up in what seems like the same time period as a few of you, I rather think that the lesson of the "super stiff aluminum" race frames (say 98-2003 give or take a couple years) was that there is such a thing as "too much" stiffness. Those frames were punishing for lighter riders.

Consider the classic CAD3 (Cipo's bike before the two As). The Lion King is a big chap. 6'2" 174 lbs (79 kilos). He requested "the stiffest frame" which considering his specialty (sprinting and fondling... wait) and size would be far too stiff for, say someone like me (who when I rode one was 143, now 149... I will make race weight again!). Chatter chatter, bump bump, hold on tight to those bars on rutted descents!

If anything, what you need is the right stiffness for speed. That will depend entirely on who you are physiologically and what you like to do on a bike. A bigger chap needs a stiffer bike than a smaller chap. A tiny, pedal dancing climber ala Pantani could get by with a much lighter, flexier bike... in fact, I'd argue that for climbing you want more of that "snap and sway" feeling. But again, it's flex in the right spots.

As far as the OP is concerned... stiffness only equals speed with those caveats. Like I said, aluminum super stiff, uncompromising frames are wonderful in the velodrome where the road is smooth and the ride is short. (Unless we are talking about the old Boulder velodrome... RIP, but that thing was sketchy as hell and rough as shit.)

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